Investigating the relationship between crash severity, traffic barrier type, and vehicle type in crashes involving traffic barrier

Interpretable machine learning for evaluating risk factors of freeway crash severity

Machine learning (ML) models are widely employed for crash severity modelling, yet their interpretability remains underexplored. Interpretation is crucial for comprehending ML results and aiding informed decision-making. This study aims to implement an interpretable ML to visualize the impacts of factors on crash severity using 5 years of freeways data from Iran. Methods including classification and regression trees (CART), K-nearest neighbours (KNNs), random forest (RF), artificial neural network (ANN) and support vector machines (SVM) were applied, with RF demonstrating superior accuracy, recall, F1-score and ROC. The accumulated local effects (ALE) were utilized for interpretation. Findings suggest that light traffic conditions (volume / capacity < 0.5 ) with critical values around 0.05 or 0.38, and higher proportion of large trucks and buses, particularly at 10% and 4%, are associated with severe crashes. Additionally, speeds exceeding 90 km/h, drivers younger than 30 years, rollover crashes, collisions with fixed objects and barriers, nighttime driving and driver fatigue elevate the likelihood of severe crashes.

An assessment of measures to reduce injuries and mortality among motorcyclists: A cross-sectional survey-based study

Background:

Motorcyclists are one of the most vulnerable groups in road accidents. This study aimed to investigate the effective measures to reduce injuries and deaths in the most vulnerable road users' motorcyclists in 2020.

Methods:

The study was a cross-sectional study. In this study, 147 motorcycles were randomly selected from the list of all motor courier units in Tehran, which was prepared through an internet search. The required information was collected through questionnaires and interviews. The inclusion criteria had a minimum high school education and an age range of 18–65 years. The trained questioners referred to the selected courier offices and after obtaining consent to participate in the study, project questionnaire were completed.

Results:

The mean age of subjects was 31.4 ± 8.0 years. All subjects were male. The purpose of the trip was going to work (84.4%). The highest percentage of leaving home time (94.6%) was observed in the morning. More than half of the subjects had a history of accidents (54.5%), and also more than half of the subjects (54.0%) had a history of an accident in their 2^nd degree relatives' families. Forth-fifths of the studied motorcyclist (89.5%) wore helmets. Nearly half of the subjects (48.3%) always fastened their helmets strap. The highest action (72.0%) was suggested to separate the motorcycle lanes.

Conclusion:

In the viewpoint of the motorcyclist, separating the motorcycle lines could be one of the most effective measurements to injury reduction. Hence, officials and planners need to pay more attention to the logical demands of motorcyclists.

Examining crash injury severity and barrier-hit outcomes from cable barriers and strong-post guardrails on Alabama's interstate highways

INTRODUCTION

This study investigates the impact of several risk factors (i.e., roadway, driver, vehicle, environmental, and barrier-specific characteristics) on the injury severity resulting from barrier-related crashes and also on barrier-hit outcomes (i.e., vehicle containment, vehicle redirection, and barrier penetration). A total of 1,685 barrier-related crashes, which occurred on three major interstate highways (I-65, I-85, and I-20) in the state of Alabama, were collected for a seven-year period (2010-2016), and all relevant information from the police reports was reviewed. Features that were rarely explored before (e.g., median width, barrier length, barrier offset or lateral position, left shoulder width, blockout type, and number of cables) were also collected and examined. Two types of longitudinal barriers were analyzed: high-tension cable barriers installed on medians and strong-post guardrails installed on medians and/or roadsides.

METHOD

Two separate mixed logit (MXL) models were used to analyze crash injury severity in median and roadside barrier-related crashes. Two additional MXL models were separately adopted for median and roadside barrier-related crashes to estimate the probability of three barrier-hit outcomes (vehicle containment, vehicle redirection, and barrier penetration).

RESULTS

The results of crash injury severity MXL models showed that, for both median and roadside barrier crashes, barrier penetration, female drivers, and driver fatigue were associated with a higher probability of injury or fatal crashes. The results of barrier-hit MXL models showed that longer barrier length, Brifen cable barrier system, and barrier lateral position were significant predictors of median barrier-hit outcomes, whereas dark lighting condition, driving under the influence (DUI), presence of curved freeway sections, and right shoulder width significantly contributed to roadside barrier-hit outcomes.

CONCLUSIONS

The MXL model succeeded in identifying several contributing factors of crash severity and barrier-hit outcomes along Alabama's interstate highways. Practical applications: One study application is to design longer barrier run length (greater than 1230 feet or 0.2 miles) to reduce the barrier penetration likelihood.

The impact of traffic barrier geometric features on crash frequency and injury severity of non-interstate highways

INTRODUCTION

The main objective of this research is to investigate the effect of traffic barrier geometric characteristics on crashes that occurred on non-interstate roads.

METHOD

For this purpose, height, side-slope rate, post-spacing, and lateral offset of about 137 miles of traffic barriers were collected on non-interstate (state, federal aid primary, federal aid secondary, and federal aid urban) highways in Wyoming. In addition, crash reports recorded between 2008 and 2017 were added to the traffic barrier dataset. The safety performance of traffic barriers with regards to their geometric features was analyzed in terms of crash frequency and crash severity using random-parameters negative binomial, and random-parameters ordered logit models, respectively.

RESULTS

From the results, box beam barriers with a height of 27-29 inches were less likely to be associated with injury and fatal injury crashes compared to other barrier types. On the other hand, the likelihood of a severe injury crash was found to be higher for box beam barriers with a height taller than 31 inches. Both W-beam and box beam barriers with a post-spacing between 6.1 and 6.3 inches reduced the probability of severe injury crashes. In terms of the crash frequency, flare traffic barriers had a lower crash frequency compared to parallel traffic barriers. Non-interstate roads without longitudinal rumble strips were associated with a higher rate of traffic barrier crashes.

Assessment of tire failure related crashes and injury severity on a mountainous freeway: Bayesian binary logit approach

Although tires maintain the only contact between the vehicle and the ground, tire failures are still underrepresented in traffic safety assessments. Vehicle stability and safety can deteriorate significantly by a sudden tire failure. The current body of literature on tire failure-related crashes is limited, and no previous study was found to extensively investigate the factors associated with tire failures and the corresponding injury severity. The contributions of this study include (i) investigating the factors affecting tire failures, (ii) assessing the impacts of tire failures on occupant injury severity, and (iii) demonstrating the necessity of statewide tire inspection regulations. An extensive exploratory analysis was performed using ten years (2007-2016) of historical crash data along I-80 in Wyoming. Binary logistic regression with the Bayesian inference approach was applied to develop two separate models: tire failure and injury severity model. The results from the tire failure model showed that vehicle speeds greater than 75 mph, commercial motor vehicles, summer season, daytime, the presence of rough surface, downgrades, and concrete pavement are all related to higher tire failure occurrences. On the other hand, the incidence of a tire failure in a crash significantly contributed to more severe injuries when combined with any of the following instances: fire or explosion, rollover, guardrail hits, runoff road, angle, rear-end, clear weather, speeding, downgrades, and curved segments. With the incorporation of the random intercept in the modeling procedure, the injury severity analysis found a strong presence (42 %) of intra-crash correlation (effects of the common crash-specific unobserved factors) in occupant injury severity within the same crash. Finally, based on the findings of the study, recommendations are provided to alleviate tire-related problems.

Estimating the effect of geometric features of side traffic barriers on crash severity of interstate roads in Wyoming

Past roadside safety studies mostly evaluated the impact of traffic barrier geometric features using simulation tools or by conducting field crash tests. While past simulation and field crash tests could present important findings for upgrading the geometric design of traffic barriers, there is still a gap regarding conducting an actual data analysis on side traffic barriers crashes with regards to their geometric dimensions. This paper aims at filling this gap by combining a statewide dataset of side traffic barrier geometric features with historical crashes on interstate roads in Wyoming. Therefore, geometric features including system height, post-spacing, lateral offset (from the edge of pavement), and side-slope of over 150 miles of side traffic barriers were inventoried by conducting a field survey on interstate roads in Wyoming. For the statistical analysis, a random-parameters ordered logit model was utilized to investigate variables impacting crash severity of side traffic barriers. It was found that system height could significantly impact the crash severity of side box beam barriers. Box beam barriers with a system height between 25 and 31 in. were identified to be less severe in comparison to other height categories, while showing minimum risks of severe crashes in the system height of 29-31 in.. On the other hand, box beam barriers with a height taller than 31 in. may increase crash severity.

Roadside Fixed-Object Collisions, Barrier Performance, and Fatal Injuries in Single-Vehicle, Run-Off-Road Crashes

Objectives: To quantify the odds of fatal injuries associated with drivers involved in single-vehicle, run-off-road (SVROR), injury crashes. Methods: An in-service safety evaluation was carried out using multivariate logistic regression models. Results: The odds of motorist death was lower for w-beam guardrail crashes as compared to tree, pole, and concrete barrier crashes. On the other hand, there was no statistically significant difference between the odds of motorist death in concrete barrier crashes as compared to tree or pole crashes. The odds of motorist death were lower for curbs and collision-free crashes as compared to tree, pole, and barrier crashes. Thus, obstacles should be removed whenever possible and barriers installed only whenever absolutely necessary. The lack of vehicle containment (in barrier crashes) was found: (i) to tend to occur on higher-posted-speed-limit roads and result in a higher percentage of fatal crashes, (ii) to be more prevalent with the less rigid barrier type, and (iii) to result in a consistently higher percentage of fatal crashes under the concrete barrier category. Conclusions: Findings not only support state-of-the-art roadside design guidelines and crash-testing criteria, but they may also be useful in evaluating proposed roadside safety improvements.